Japanese Patent Application Laid-Open No. Hei 8-97969 (Hereinafter referred to as Patent Document 1) discloses a scan type display device having an image scanning function. This scan type display device includes a light-emitting cell array and a light-receiving element. The light-emitting cell array is constituted with numerous light-emitting cells arranged linearly. Light radiated by the light-emitting cell, after being reflected on a surface of a shielding object, is made incident on the light-receiving element. The scan type display device turns on a plurality of light-emitting cells one by one sequentially, and scans an image based on an output of the light-receiving element. This scan type display device reads out image data stored in a memory sequentially by a predetermined amount, and on/off drives the light-emitting cell array according to the data. A user holds in a hand and swings this scan type display device, to form a two-dimensional image by a residual image effect.
However, this conventional residual image display device disclosed in the Patent Document 1 has various problems as follows.
A first problem is as follows. The conventional image display device makes the light-emitting cells emit light in sequence to perform scan processing of an image. Therefore, a size of the image to be scanned is required to be adjusted to a size of the array of the light-emitting cells. Namely, in order to make the conventional residual image display device scan an image, it is necessary to make the image into the size adjusted to an array length of the plural light-emitting cells.
A second problem is as follows. The conventional image display device makes the light-emitting cells emit light to form a two-dimensional residual image. In order for the scanned image to be viewed as one residual image, light-emission of the light-emitting cells by the scanned data is required to be completed within a time being able to be viewed as one residual image. Therefore, in order for the scanned image to be viewed as one residual image, it is necessary to make the size of the image to be scanned into equal to or smaller than a size that can be viewed as one residual image.
A third problem is as follows. The conventional residual image display device is swung with the light-emitting cell array being faced to a person to be shown. Therefore, a person who holds in hand and swings the residual image display device cannot see the light-emitting cell array. The person who holds in hand and swings the residual image display device can not check whether the scanned image is viewed as one residual image or not.
A fourth problem is as follows. In the conventional residual image display device, the light-emitting cell in a displaying part turns on. The light-emitting cell in a non-displaying part turns off. Therefore, if the conventional residual image display device scans a line drawing, a letter, or the like, light-emitting cells that turn on are small in number. Consequently, it is difficult for an observer to recognize what kind of line drawing or letter is displayed. If the behind of the person who holds in hand and waves the residual image display device is bright, the lights from the light-emitting cells are buried in the brightness of the background, and it is hard for the observer to recognize the image.
The present invention is made in view of the above problems and is to solve one of the various problems in the conventional residual image display device using a plurality of light-emitting diodes, and thereby is to obtain a residual image display device easier to use than the conventional residual image display device.